The present invention relates to superconductive compounds which show superconductive characteristics in multiple phases at temperatures ranging from approximately 14 K. to 310 K. More particularly, this invention relates to a process for predicting the superconductive properties of compounds and identifying the most significant compounds which are superconductive by ambient temperatures, and to a process for the production of said compounds.
The recent discovery of high transition temperature superconductors represents a possible technological revolution and has attracted the interest of scientists from around the world. These new materials are ceramics, made from metal oxides.
During the past two years, many studies have been reported following the discovery of the efficacy of La--Ba--Cu--O materials. This system has been extensively analyzed and has a transition temperature around 30 K. Subsequently a Y--Ba--Cu--O material having a 90 K. transition temperature was obtained. Many other 90 K. superconducting materials have been obtained substituting a rare earth element for the yttrium.
From X-Ray studies the crystalography of these 90 K. compounds is well known. These superconductors (R--Ba--Cu--O, R=Y, rare earth) have been called 1,2,3 compounds because of their stoichiometry and present an orthorhombic unit cell, which can be visualized as a stacking of three perovskites.
Compounds based on bismuth (Bi--Sr--Cu--O) which show superconductive characteristics with transition temperatures in the range from 90 K. to 120 K. have also been reported. The bismuth-based compounds have been modified by adding calcium, producing superconductive ceramic compounds of the type Bi--Sr,Ca--Cu--O.
From the point of view of possible applications of these materials, it is important to emphasize that they are superconductors above the liquid nitrogen temperature. However, an increase in their transition temperature widens technological possibilities even more.
As it can be inferred from the above, the technology developed so far is greatly limited by the fact that, in order to achieve the phenomenon of superconductivity, it is necessary to cool the materials by means of liquid nitrogen, which represents a serious limitation as to the possibility of using such materials for practical applications. Hence, ongoing research has focused on the development of superconductive materials which can operate efficiently at higher temperatures, ideally at ambient temperatures.
All of these ceramic materials are produced through solid state reactions of appropriate amounts of the original oxides. Nevertheless, what determines the quality and characteristics of the products, other than their composition, are the times, temperatures and conditions involved in each step of the process, as well as the number of times the steps are repeated. In the past the primary method of identifying materials having the best superconductive properties has been by trial and error.